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Table Of Contents
50
Lesson 10 Driving LEDs by 74HC595
Introduction
In this lesson, we will learn how to use 74HC595 to make eight LEDs blink regularly.
Components
- 1 * Raspberry Pi
- 1 * Breadboard
- 1 * 74HC595
- 8 * LED
- 8 * Resistor (220Ω)
- Jumper wires
Principle
74HC595
The 74HC595 consists of an 8−bit shift register and a storage register with three−state
parallel outputs. It converts serial input into parallel output so that you can save IO ports of
an MCU. The 74HC595 is widely used to indicate multipath LEDs and drive multi-bit segment
displays. "Three-state" mentioned above refers to the fact that you can set the output pins
as either high, low or high impedance. With data latching, the instant output will not be
affected during the shifting; with data output, you can cascade 74HC595s more easily.
Compatible with low voltage TTL circuit, 74HC595 can transform serial input of 8-bit data
into parallel output of 8-bit data. So it is often used to extend GPIO for embedded system
and drive low power devices.
Pins of 74HC595 and their functions:
Q0-Q7: 8-bit parallel data output pins, able to control 8 LEDs or 8 pins of 7-segment display
directly.